4 research outputs found
Dually Active Silicon Nanowire Transistors and Circuits with Equal Electron and Hole Transport
We
present novel multifunctional nanocircuits built from nanowire transistors
that uniquely feature equal electron and hole conduction. Thereby,
the mandatory requirement to yield energy efficient circuits with
a single type of transistor is shown for the first time. Contrary
to any transistor reported up to date, regardless of the technology
and semiconductor materials employed, the dually active silicon nanowire
channels shown here exhibit an ideal symmetry of current–voltage
device characteristics for electron (n-type) and hole (p-type) conduction
as evaluated in terms of comparable currents, turn-on threshold voltages,
and switching slopes. The key enabler to symmetry is the selective
tunability of the tunneling transmission of charge carriers as rendered
by the combination of the nanometer-scale dimensions of the junctions
and the application of radially compressive strain. To prove the advantage
of this concept we integrated dually active transistors into cascadable
and multifunctional one-dimensional circuit strings. The nanocircuits confirm energy efficient switching and can further be electrically configured to provide four different types of operation modes compared to a single one when employing conventional electronics with the same amount of transistors
Catalytic Janus Motors on Microfluidic Chip: Deterministic Motion for Targeted Cargo Delivery
We fabricated self-powered colloidal Janus motors combining catalytic and magnetic cap structures, and demonstrated their performance for manipulation (uploading, transportation, delivery) and sorting of microobjects on microfluidic chips. The specific magnetic properties of the Janus motors are provided by ultrathin multilayer films that are designed to align the magnetic moment along the main symmetry axis of the cap. This unique property allows a deterministic motion of the Janus particles at a large scale when guided in an external magnetic field. The observed directional control of the motion combined with extensive functionality of the colloidal Janus motors conceptually opens a straightforward route for targeted delivery of species, which are relevant in the field of chemistry, biology, and medicine
Thermal Conductivity of Mechanically Joined Semiconducting/Metal Nanomembrane Superlattices
The decrease of thermal conductivity
is crucial for the development
of efficient thermal energy converters. Systems composed of a periodic
set of very thin layers show among the smallest thermal conductivities
reported to-date. Here, we fabricate in an unconventional but straightforward
way hybrid superlattices consisting of a large number of nanomembranes
mechanically stacked on top of each other. The superlattices can consist
of an arbitrary composition of n- or p-type doped single-crystalline
semiconductors and a polycrystalline metal layer. These hybrid multilayered
systems are fabricated by taking advantage of the self-rolling technique.
First, differentially strained nanomembranes are rolled into three-dimensional
microtubes with multiple windings. By applying vertical pressure,
the tubes are then compressed and converted into a planar hybrid superlattice.
The thermal measurements show a substantial reduction of the cross-sectional
heat transport through the nanomembrane superlattice compared to a
single nanomembrane layer. Time-domain thermoreflectance measurements
yield thermal conductivity values below 2 W m<sup>–1</sup> K<sup>–1</sup>. Compared to bulk values, this represents a reduction
of 2 orders of magnitude by the incorporation of the mechanically
joined interfaces. The scanning thermal atomic force microscopy measurements
support the observation of reduced thermal transport on top of the
superlattices. In addition, small defects with a spatial resolution
of ∼100 nm can be resolved in the thermal maps. The low thermal
conductivity reveals the potential of this approach to fabricate miniaturized
on-chip solutions for energy harvesters in, e.g., microautonomous
systems
Confirming the Dual Role of Etchants during the Enrichment of Semiconducting Single Wall Carbon Nanotubes by Chemical Vapor Deposition
The search for ways
to synthesize single wall carbon nanotubes
(SWCNT) of a given electronic type in a controlled manner persists
despite great challenges because the potential rewards are huge, in
particular as a material beyond silicon. In this work we take a systematic
look at three primary aspects of semiconducting enriched SWCNT grown
by chemical vapor deposition. The role of catalyst choice, substrate,
and feedstock mixture are investigated. In terms of semiconducting
yield enhancement, little influence is found from either the binary
catalyst or substrate choice. However, a very clear enrichment is
found as one adds nominal amounts of methanol to an ethanol feedstock.
Yields of up to 97% semiconducting SWCNT are obtained. These changes
are attributed to two known etchant processes. In the first, metal
SWCNT are preferentially etched. In the second, we reveal etchants
also preferentially etch small diameter tubes because they are more
reactive. The etchants are confirmed to have a dual role, to preferentially
etch metallic tubes and narrow diameter tubes (both metallic and semiconducting)
which results in a narrowing of the SWCNT diameter distribution